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Backdoor Roth IRA Calculator

Planning a backdoor Roth IRA? Enter your nondeductible contribution, the amount you're converting and your year-end pre-tax IRA balances to see how much of the conversion is taxable under the pro-rata rule, line by line as on Form 8606. Then work out your 2026 mega backdoor Roth room in your 401(k).

Updated November 4, 2026. Free, no sign-up; everything runs in your browser and nothing you type is stored.

Backdoor Roth IRA calculator (Form 8606 pro-rata rule)

Nondeductible IRA contribution for 2026 ($)Basis from earlier years, Form 8606 line 14 ($)Amount converted to Roth ($)

Dec 31, 2026 value of all traditional, SEP and SIMPLE IRAs, after the conversion ($)Other IRA withdrawals in 2026 ($)Your top tax rate (%)

–Taxable amount of the conversion

–Estimated federal tax on it

–Share of conversion taxed

Mega backdoor Roth calculator (2026 401(k) limits)

If your 401(k) accepts after-tax (non-Roth) contributions and lets you convert them, you can fill the gap up to the $72,000 total limit and move it to Roth.

Your age at the end of 2026Your 401(k) deferrals, pre-tax + Roth ($)Employer match and profit sharing ($)Your pay from this employer ($)

–After-tax room for a mega backdoor Roth

–Catch-up

–Total into the 401(k)

How a backdoor Roth IRA works

For 2026, direct Roth IRA contributions phase out between $153,000 and $168,000 of MAGI for single filers and $242,000–$252,000 for joint filers.
Anyone with earned income can still make a nondeductible traditional IRA contribution (up to $7,500, or $8,600 at 50+), then convert it to a Roth IRA. There's no income limit on conversions.
Report the contribution and the conversion on Form 8606. The table above follows its lines.

The pro-rata rule

The IRS treats all your traditional, SEP and SIMPLE IRAs as one pot. If you convert $7,500 of after-tax money but also hold $67,500 of pre-tax IRA money on December 31, only $7,500 ÷ $75,000 = 10% of the conversion is tax-free; the other 90% is taxed as income. The balance is measured on December 31 of the conversion year, so rolling pre-tax IRAs into a 401(k) before year end can fix it. Roth IRAs and 401(k)s don't count toward the pro-rata calculation.

2026 limits for the mega backdoor Roth

Limit	2026
Employee deferrals (pre-tax + Roth)	$24,500
Catch-up, age 50+	$8,000
Catch-up, ages 60–63 (if the plan allows)	$11,250
Total from all sources, section 415(c)	$72,000 (catch-up is extra)

Common questions

Is a backdoor Roth IRA legal?

Yes. Nondeductible contributions and Roth conversions are both allowed by the tax code, and the conversion has had no income limit since 2010. Report both on Form 8606.

How does the pro-rata rule affect a backdoor Roth?

If you have pre-tax money in any traditional, SEP or SIMPLE IRA on December 31, part of your conversion is taxable in proportion to that balance.

How much can I put in a mega backdoor Roth in 2026?

Up to $72,000 minus your own deferrals and employer contributions. With $24,500 of deferrals and an $8,000 match, that leaves $39,500 of after-tax room, if your plan allows it.

When should I convert after a nondeductible contribution?

Many people convert soon after contributing so little or no taxable growth builds up first. Any earnings before conversion are taxable.

Do I need Form 8606 every year?

File it for any year you make nondeductible IRA contributions or take distributions or conversions from IRAs with basis.

Sources

General information, not financial, tax or legal advice. Check important numbers with the official source before acting on them.